To evaluate messages about infant feeding on breastmilk substitute (BMS) manufacturer websites directed at US caregivers and compare information and portrayals of breast-feeding/breastmilk with that of infant formula (IF) feeding.

We conducted a content analysis of US BMS companies’ websites. A codebook was created through an iterative process to identify messages and images about breast-feeding/breastmilk and IF feeding, including benefits or issues associated with each, and direct-to-consumer marketing practices that could discourage breast-feeding.

Data were collected in 2019–2020 and analysed in 2020–2021 for US websites of five IF manufacturers.

The websites of Similac, Enfamil and Gerber, which collectively represent approximately 98 % of the US IF market, and two US organic brands, Earth’s Best and Happy Baby.

Websites contained more messages about breast-feeding/breastmilk than IF but were significantly more likely to mention benefits to baby of IF (44 %) than breast-feeding/breastmilk (<26 %), including significantly more statements that IF provides brain, neural and gastrointestinal benefits; 40 % of breast-feeding/breastmilk content was dedicated to breast-feeding problems (e.g. sore nipples). Twice as many screenshots compared IF brands favourably to breastmilk than as superior to other brands. Certain companies displayed images indicating ease of IF feeding and difficulty of breast-feeding.

Substantial messaging on BMS manufacturer websites encouraged IF feeding and discouraged breast-feeding. Health professionals should discourage their patients from visiting these websites and the US government should regulate misleading claims. Companies should refrain from providing breast-feeding advice and align their US marketing with the International Code of Marketing of Breast-milk Substitutes.